a cougar (if the girl is older)
Cradle-Snatching, or Cradle-robbing, especially if the younger person is a teenager. More generally, this is known as a May-December relationship.
Paedophilia. It is called paedophilia.
YOUNGER
yes
This describes a positive relationship.
Cradle Robber edit: cradle robber is for either sex dateing a younger than legal age person. Sugar Daddy is older guy with younger woman. other answers are: lucky ba$t4rd horny old goat pervert
A grave robber, perhaps. A "Craddle Snatcher" is one who develops a relationship with another who is much younger. The opposite would be a younger person who seeks relationships with someone markedly older.
The cons of an older woman younger man relationship are very much subjective and about the tastes of the individual. Generally she will age faster meaning they might have less in common and he will be more likely to be drawn to younger women later.
Younger women who like older men are simply called cheetah. Since when a younger girl goes after an older man they try and get with him just as fast as a cheetah would catch its prey in the wild.
baby chicken
its called a pair
There is no law prohibiting this unless the older person is in a position of authority over the younger person. (such as a teacher, counsellor, coach, etc) In such case it is against the law if the younger person is under the age of 18.